On the Watts Up With That site it is worth tracking through the tree ring discussions and reading the guest article:
http://wattsupwiththat.com/2009/10/02/a-hands-on-view-of-tree-growth-and-tree-rings-one-explanation-for-briffas-yad061-lone-tree-core/

I call them simply fraudulent. Without being educated in whatever science they are supposedly experts at, I could take a look at those tree cores and quickly pick out ones which ones showed wider rings in any sequence desired, and select those which would seem to show whatever I wanted them to show.

This should give members something to think about, (and check for themselves):-

I recently had to cut down an old Oak Tree on my property; what was very noticeable was the huge radial variation in the growth ring width, leading me to the conclusion that Ring is the wrong term: contour maps would be more appropriate? Clearly, not all trees grow in even concentric circles! --- I can think of several reasons as to why this comes about. --- The tree's main tap roots on one side have better access to water and nutrients. / If the tree is growing on a slope, increased growth is likely on the downhill side. / If the tree grows in the face of strong prevailing winds, increased growth is likely on the lee side. / If the tree throws out a heavy limb, that side could increase its growth to feed it.

If you were to now take six core samples around the circumference of such a tree, you would get six wildly different results! And another tree could be different again, and again, and again? As the usual practice is to take one core from each of many trees, how do they decide where to 'stick it'?

Methinks that Larry is absolutely right, anybody can make the facts fit the interpretation. Using tree growth ring widths to assess Global Climate is impossible. However, they will give a good clue to the tree's prevailing micro climate, its micro environment, and its unique growth history.

The basic assumption regarding tree growth rate being subject to variations of temperature was that the leaves/needles would be at ambient air temperatures. When the ambient air temperatures were cooler, the process of photosynthesis would slow, and there would thus be less tree growth at lower air temperatures, and more tree growth at higher air temperatures.

New research from biologists at the University of Pennsylvania, however, shows that trees, sampled from boreal climates to subtropical climates, maintain the temperature of their leaves to a fairly constant temperature. Ambient air temperatures have little or no effect on the temperatures of the leaves themselves.

Since the basic assumption underlying the "theory" that ambient air temperatures have a significant effect on tree growth is thus falsified, the use of tree growth as indicated by tree rings as a proxy for temperature should be entirely discarded, and the proxies that have been calculated previously should be reported as useless, and deleted from any further consideration. These findings should, of course, be verified by studies by others first.

We know that more CO2 means better plant growth, so presumably that applies to trees also. More CO2 = more growth = wider tree rings. If that is the case, then we would expect to see very good correlation between tree ring width and CO2. Only that has nothing to do with temperature.

Wonderful to see real science in operation. The WGAW's will just have to face the fact that Nature has been at the game of climate adaptation for a few billion years or so. If us mere humans think that we can hoodwink or second guess it, we are on a 'hiding for nothing'. Trees have been at the game for long enough to get it right, 'they' are forced to bend to the eternal Laws of Physics.

What is illuminating about this study of photosynthesis in trees, is the equilibrium temperature which is maintained by the Process: it confirms my own theories which started to take shape in the early 60's. I was, at the time, engaged in a study of methane digesters for biogas production (on a chicken farm), very smelly! The key to the economics of the operation was to determine the energy input required during the cold season, and the cooling energy output during the warm season, as anaerobic bacterial activity must be held between 35 and 39 C, --- 37 C being the optimum. As this is identical to the the body core temperature maintained by humans, and we are just a mobile stomach with anaerobes in a digestive gut, I considered that I had learned something important about how, and why, nature optimises chemical processes at temperatures to suit the prevailing environment.

Now cycle 20 years on to the early 80's. To further my combustion research, I was then studying plant physiology in order to understand the conversion of Carbon Dioxide to Carbo-Hydrates and Hydro-Carbons at very low temp. and atmos. pressure. (At the same time I was making cross comparisons with the well known Steam Re-forming process, i.e. Hydrogenation of Syn-Gas (CO) and CO2, which operates at very high temp. and pressure). In plants, the Exothermic side of the process is initiated by the magic of photosynthesis, but the Endothermic (hydrogenation) side is controlled by a plant's access to water. The optimum temperature of the process then, is determined not by photosynthesis, but by the bio-chemistry of plant life, which works best at around 21 C, (very close to the ideal for our external surfaces)?

Thus I can confirm but from a very different direction, that Trees, like all our plant life, are no more dependent on the atmospheric temperature ambient for their growth rate than we humans are. They, like us, are wholly dependent on Water, both for life's essential chemical processes and its thermal equilibrium, (heat exchange via evaporative cooling). --- Consequently, from a scientific point of view, 'Tree Rings' as a proxy for climate temperature have as much relevance as 'Tea Leaf' patterns in a tea cup!

Trust the above helps to dispel the AGW myths, but really, if you want to know what controls the growth rate of plants? --- Just ask any farmer.